The goal of the Adherence and Retention Core (ARC) is to provide consultation and advice on strategies to promote adherence and increase retention in order to enhance successful completion of clinical studies of balance and mobility. Related to this is the goal of improving measurement of adherence and retention within clinical studies to facilitate the interpretation of treatment outcomes as well as to examine the moderation of outcomes by level of patient participation. Current research on adherence demonstrates poor adherence with behavioral and pharmacologic treatment regimens even among well elders, with as up to 50% of patients not following pharmacological regimens and as few as 25% of patients continuing prescribed exercise regimen at one year. Little is known about adherence with balance exercise in mobility impaired older adults. Poor adherence attenuates treatment outcome relationships, thus reducing the ability to detect treatment effects as well as treatment side effects. Subject retention is also a significant problem. Loss of subjects poses significant threats to power within studies and is particularly problematic when biases occur in drop out rates. Loss of subjects may attenuate the delivery of intervention through early termination of treatment and/or may contribute to significant loss of data at the end of the trial. In either case, power is lost within the study. Efforts to enhance adherence and retention are important components of clinical trial design and conduct. The purpose of the Adherence and Retention core will be to consult and advise investigators within the center on strategies and techniques to prevent adherence and retention problems in OAIC projects as well as to provide advice and consultation on improving adherence and retention should ongoing studies find that these rates are suboptimal. The Specific Aims of the Adherence and Retention Core are to: 1. Provide consultation and advice to investigators regarding the design and development of adherence and retention components of new projects and the support of ancillary studies addressing adherence and retention issues in ongoing funded projects; as well as advice on the improvement of retention and adherence in ongoing studies; 2. Provide access to relevant literature on assessment strategies and intervention protocols as well as general literature on adherence through the maintenance and enhancement of a library of such resources, and access to assessment technologies for evaluation and training purposes; 3. Develop new strategies and technologies beyond the current capabilities of the existing knowledge, addressing the unique needs of the older adult through the design and conduct of developmental studies; and 4. Support the research training mission of the OAIC through the training of investigators and staff in the impact of poor adherence and retention on interpretation of study outcomes; the use of strategies and technology to promote adherence and retention; and measurement strategies for assessing adherence and retention in clinical studies.